These are certainly not a beginner's product, their small size makes it difficult to isolate the feeling of them inside you and clench the muscles around them. Although the product page says they are plastic, when they arrived they appear to be metal which makes them much heavier and more durable then one would expect. While they are still a little more difficult than I am ready for I like that I have them and am working up to holding them both internally for long periods of time.
The most helpful critical review
These balls fell out within less than a minute of insertion (although I am very tight). They have no bells, provide no vibrations, and contain some kind of metal rather than the plastic listed on the product page.